We have defined some of the effects of oxygen-derived free radical compounds (ODFRC) (viz, superoxide, hydroxyl, singlet oxygen and hydrogen peroxide) in inflammation by sing three in vitro models of inflammatory cellular interactions. We have shown that the radical scavenger, reduced glutathione is a major positive determinant of the ability of murine spleen cells to produced an antibody response, in vitro. We have found that the enhancement of the antibody response by 2-mercaptoethanol is also mediated by glutathione. These enhancement effects can be mimicked by the addition of other known scavengers of ODFRC. Macrophages, stimulated in vivo, can suppress lectin-induced lymphocyte proliferation and serum-induced fibroblast proliferation. The use of inhibitors of prostaglandin synthesis and scavengers of ODFRC has provided evidence that the suppression of lymphocyte proliferation by macrophages is produced by a synergy of prostaglandins and ODFRC; similar experiments have provided evidence that the suppression of fibroblast proliferation by macrophages is mediated by ODFRC alone. Thus ODFRC appear to be important in the modulation of inflammatory cellular interactions.